Combination caustic and hydrorefining process



Feb. 6, 1968 A g, ALDRIDGE ET AL 3,367,861

COMBINATION CAUSTIC AND HYDROREFINING PROCESS Filed Sept. 5, 1965Scrzabber 4 l3 2 6 Separator Feed 7 I g 7 -7 KOH 8 Chem/calDesu/fun'zafion Zone 60 2 /a 5 H 0 Ad us/men/ I Zone t g 20 Product 1 l2g Hydradsu/funkaflbn 7 Regenerafian Zone Zone steaming Zane CL YDE L.ALDR/DGE RALPH B. MASON um vs GLEN R HAMMER PATENT Arr'omvrr UnitedStates Patent Office 3,367,861 Patented Feb. 6, 1968 3,367,861CGMBINATEUN CAUSTIC AND HYBRU- REFINING lROCESS Clyde L. Aldridge andGlen P. Hammer, Baton Rouge, and Ralph Burgess Mason, Denham Springs,1.2., as= signors to Esso Research and Engineering Company, acorporation of Delaware Filed Sept. 3, i065, Ser. No. 484,906 3 Claims.(Cl. 203-211) This invention relates to a process for the removal ofsulfur from liquid hydrocarbon streams, particularly petroleumresiduu-ms. More specifically, the invention relates to an integratedtwo-stage desulfurization process cornprising chemical desulfurizationin the first stage and hydrodesulfurization in the second stage.

Generally, sulfur occurs in petroleum stocks in one of the followingforms: mercaptans, sulfides, disulfides and as part of a more or lesssubstituted ring of which thiophene, benzothiophene and dibenzothiopheneare the prototypes. The mercaptans are generally found in the lowerboiling fractions, e.g. the naphtha, kerosene, and light gas oil.Numerous processes for sulfur removal from these lower boiling fractionshave been suggested, such as doc tor sweetening (wherein mercaptans areconverted to disulfides), caustic treating, solvent extraction, copperchloride treating, etc., all of which give a more or less satisfactorydecrease in sulfur or inactivation of mercaptans by their conversioninto disulfides. When the process results in the latter effect, thedisulfides generally remain in the treated product and must be removedby another step if it is desired to obtain a sulfur-free product.

Sulfur removal from higher boiling fractions, however, has been a muchmore difficult operation. Here the sulfur is present for the most partin the less reactive forms as sulfides, disulfides and as a part of aring compound, such as thiophenes, benzothiophenes anddibenzothiophenes. Such sulfur is, of course, not susceptible tochemical operations satisfactory for removal of mercaptans. Extractionprocesses employing sulfur-selective solvents are also unsatisfactorybecause the high boiling petroleum fractions contain such a highpercentage of sulfur-containing molecules. For example, even if aresiduum contains only about 3% sulfur it is estimated thatsubstantially all the molecules may contain sulfur. Thus, if such aresiduum were extracted with a solvent selective to sulfur compounds thebulk of the residuum would be extracted and lost.

Metallic contaminants, such as nickel and vanadium compounds, are foundas innate constituents in practically all crude oils. These contaminantspresent another problem. Upon fractionation of the crudes, the metalliccontaminants are concentrated in the residua which normally have initialboiling points of about 500 F. Such residua are conventionally used asheavy fuels, and it has been found that the metal contaminants thereinadversely affect the combustion equipment in which the residua areburned. The contaminants not only for mash, which leads to sludging andthe formation of deposits upon boiler tubes, combustion chamber walls,and gas turbine blades, but also attack the refractories which are usedto line boilers and combustion chambers and severely corrode boilertubes and other metallic surfaces with which they come into contact athigh temperatures.

The nitrogenous compounds are found in many crude oils to a varyingextent depending on the source. These compounds are objectionableprimarily due to (1) their tendency to promote instability in thefinished, marketable products, such as gasoline, kerosene, heating oil,jet fuels and the like regardless of whether these are obtained bysimple distillation procedures or by cracking heavier fractions and (2)due to their adverse effects on the activity of catalytic materials usedin cracking reactions, etc.

In the past, methods to chemically remove the sulfur have beenineffective to remove large amounts of sulfur and furthermore, hadlittle or no effect on the nitrogenous or metallic impurities, thesematerials requiring other methods for their removal.

A process for the chemical desulfurization of residuum stocks employingfused alkali metal hydroxides has been disclosed by Mattox in US. Patent3,164,545 issued J an. 5, 1965. The disclosed process is also effectiveto remove nitrogen compounds and metallic contaminants. Whilecontaminant removal is excellent using fused alkali metal hydroxides,the process suffers from the inherent defect that the treating agentbecomes spent and it must be regenerated.

Process for hydrodesulfurizing oils in the presence of a catalyst arewell known in the petroleum refining art. It is also well known thatmost of the present processes are limited to feeds which contain lowamounts of sulfur, and nitrogen compounds and metal contaminants. Suchpretreatments as solvent deasphalting and vacuum distillation are usedto reduce sulfur, nitrogen and metals to a level so that thehydrodesulfurization catalyst. is not rapidly poisoned.

The object of this invention is to provide a process for thedesulfurization of heavy oils which does not require extensive feedconditioning or expensive and complicated pretreating steps. It isanother object of this invention to provide a combined chemicaldesulfurization-hydrodesulfurization process in which the disadvantagesof each type of treatment are alleviated by coordinating the twotreatments.

We have found that essentially untreated heavy oils such as whole crudeoils, topped crude oils, atmospheric residuums, shale oils and the likecan be treated with fused alkali metal hydroxides to remove aconsiderable amount of the sulfur and nitrogen compounds and the metalcontaminants and the partially refined hydrodesulfurized without rapidpoisoning of the catalyst. Furthermore We have found that the H 3 formedin hydrodesulfurization can be used to regenerate the spent alkali metalhydroxide treating agent.

The invention will be further illustrated by the accompanying drawingwhich is a schematic flow sheet showing a preferred method forpracticing the process of the invention.

Reference numeral 1 denotes a line supplying a feed of the typedescribed above to chemical desulfurization zone 2. A typical feed isKuwait 450 F. topped crude, i.e. material boiling less than 450 F. hasbeen removed from the crude by distillation at atmospheric pressure. Thefused alkali metal hydroxide treating agent, KOH for example, is addedto zone 2 by line 3. The quantity of KOH will range from 5 to wt.percent based on the feed. The preferred quantity of KOH ranges from 5to 30 wt. percent.

The amount of Water in the molten alkali metal hydroxide is importantfor the improved results of the in stant invention. The water contentshould be within the range of about 5 to 30 wt. percent based on totalreagent, preferably 7 to 25 wt. percent, and more preferably 10 to 20wt. percent. The most preferred water content is about 15 wt. percent,based on molten alkali metal hydroxide. Temperature conditions duringthe contacting step should be maintained within the range of 400 to 800F., preferably 450 to 750 F., more preferably 500 to 700 F. Treatingtime may be as little as hour to 16 hours, generally the longer the timeof contact, the greater the impurity removal. Generally, treating timeswithin the range of A1 to 6 hours are used. The preferred treating timeper stage will be /2 to about 2 hours. The pressure may vary from to 500p.s.i.g., depending on the hydrocarbon feedstock, and is not critical tothe desulfurization reaction.

A small quantity of hydrogen produced in the treating step is removed byline 4 for use in the process or for other refinery operations.

The mixture of KOH and treated residuum leaves the treating zone throughline and is mixed with about 0.5 to 3 weights of Water per weight oftreating agent used and passes to separator 7. The separator can be aconventional settler in which the mixture of molten alkali metal, thereaction products of the feed impurities with the treating agent, andthe water separate as a distinct phase from the treated residuum.

The treatment with KOH removes from -60% of the sulfur and a majoramount of the nitrogen and metal contaminants from the oil. A Kuwaittopped crude was treated with 100 wt. percent KOH at 650 F. for 4 hoursresulting in a decrease of sulfur content from 2.9 wt. percent to 2.1Wt. percent and vanadium content was reduced from 31 p.p.m. to 2.5p.p.m. It is the consensus of experts that it is the metals, especiallythe vanadium found in many crude oils which severly limit catalyst lifein treating residuum and thereby makes hydrodesulfurization of untreatedresidua impractical. Therefore, it can be seen that the molten alkalimetal treating step of the invention which removes both sulfur andmetals is a valuable tool for preparing stocks for hydrodesulfurization.

The demetallized and partially desulfurize-d residuum is then passed byline 8 to hydrodesulfurization zone 9. Hydrogen is added by lines 10 and11. The hydrodesulfurization treatment is carried out in theconventional manner with known catalysts. Desulfurized product is removed by line 12. Suitable process conditions are:

Feed rate, v./v./hr. 0.2 to 2.0 Hydrogen rate, s.c.f./bbl. 500 to 6000Pressure, p.s.i.g 300 to 3000 Temperature, F 550 to 900 Preferredcatalysts are 5-15 wt. percent molybdena on porous alumina and mixturesof cobalt oxide (3-6 wt. percent) with molybdenum oxide (6-12 wt.percent) on adsorptive alumina. Catalysts containing nickel, chromia,platinum, and tungsten in the form of metals, oxides and sulfides onalumina, charcoal, kieselguhr, and bauxite can be used as well.

A gas comprising H and H 8 is carried overhead from thehydrodesulfurization zone by line 13 and the H S is removed by aconventional gas separation process such as amine scrubbing in scrubber14. Hydrogen is recycled by lines 15 and 11.

From 95% of the sulfur in a topped crude can be removed by the two-stagetreating process of our invention. If desired, more severehydrodesulfurization conditions can be employed since the metals havebeen removed from the hydrodesulfurization feed.

H S from the gas scrubber 14 is passed by line 16 to zone 17 for use inregeneration of the spent alkali metal treating agent from the firsttreating step. When KOH is used as the treating agent, the spentmaterial contains unreacted KOH, K 8, K CO and Water. Considering theKOH, K 5 and K CO as a basis the K CO constitutes from 10 to 65 wt.percent of these materials. It is the most diflicult material toregenerate. The spent material is passed by line 18 t0 regeneration zone17 and contacted with H 5 at a temperature ranging from 200 to 750 F.and at atmospheric, subatmospheric, or elevated pressures, preferably 1to 500 p.s.i.a. An excess of H 3 based on the K CO and 5 is employed.The carbonate and the K 8 are converted to KSH by this regeneration.treatment according to the following reaction:

CO is removed by line 19. A 35 wt. percent aqueous solution of K CO wascontacted by bubbling H 8 through the solution at 217 F. and atmosphericpressure. The off gas contained 50% CO demonstrating a conversion of78%. This result was unexpected since H S is weaker acid than CO (aq.).

In the afo:ementioned regeneration step K 8 is converted to KSH.

A stream containing KSH, and Water is passed by line 20 to a secondregeneration zone 21 in which the KSH is converted to KOH, the desiredalkali metal hydroxide chemical desulfurization agent. This conversioncan be accomplished by a number of methods, one of which com prisestreating with steam at a temperature ranging from 400 to 1000 F. Steamis'introduced to zone 21 by line 22. Unreacted steam and H 8 are removedby line 26. Regenerated KOH is passed by line 23 to H O adjustment zone24. In zone 24 the water content of the KOH treating agent is adjustedto a range of about 5 to 30 wt. percent based on the total reagent usedin zone 2. The treating agent is then recycled by line 25 and 3 to thetreating zone. Frequently it is desirable to follow the steaming stepwith a treatment of the caustic solution by a metal or metal oxide suchas Cu or CuO, Fe or Fe O etc. to ensure good removal of the sulfur andcomplete caustic regeneration.

Thus it can be seen that the present invention discloses a two-stagedesulfurization system in which the chemical desulfurization stagebenefits the hydrodesulfurization stage by removing metals, nitrogen,and sulfur and the hydrodesulfurization stage benefits the chemicaldesulfurization stage by providing H 8 for regeneration of the moltenalkali metal treating agent.

The overall process provides the capability of desulfurizing sulfurcontaining feedstocks without the necessity for extensive p-retreatingsuch as deasphalting and vacuum distillation.

The products of the present invention can be used as industrial fuels,as feed to catalytic cracking processes and as feed to hy-drocrackingprocess or in any other area of utility where it is mandatory that thestock being used or treated be low in sulfur, nitrogen and metalscontent.

The molten alkali metal hydroxides suitable for use in carrying out theprocess of the invention include molten sodium hydroxide, potassiumhydroxide, lithium hydroxide, cesium hydroxide and the like. KOH is thepreferred treating agent and it can be promoted with any of theaforementioned alkali metal hydroxides.

In a particularly preferred embodiment of the invention, the moltenalkali metal having the aforementioned water content of 5 to 30 wt.percent is employed in the presence of an oxygen-containing gas. It hasbeen found that the addition of oxygen during the chemicaldesulfurization stage results in a surprising increase in the amount ofcontaminants removed from the residuum. Generally it is preferred tosupply the oxygen by bubbling air or a similar oxygen-containing gasthrough the feed during treatment with the fused hydroxide. When air isused, air rates of from 1 to 1500 standard cubic feet per barrel ofresiduum can be used. Spargers, distribution plates or otherconventional means, not shown in the drawing can be used to promotecontacting of the oxygen and the oil.

In a further modification of the present invention the alkali metalbisulfide treated in zone 21 is converted to the alkali metal hydroxidephase by contacting the alkali metal bisulfide at temperatures rangingfrom 200-1000" F. with a finely-divided metal (Me), metal oxide (MeO) ormetal hydroxide (MeOH). The metal sulfides can be converted back to themetals, metal oxides or hydroxides by known methods. Suitable metalsinclude copper, nickel, iron, manganese, cobalt, calcium, magnesium,molybdenum, lead, tin and Zinc. Oxides or hydroxides of these metalswould also be suitable. Copper and iron and the oxides and hydroxidesthereof are the preferred metals.

Where their use is deemed advisable solvents, diluents and solutizerscan be used to thin the residuum so that contacting will be morecomplete.

The molten alkali metal treating stage and the hydrodesulfurizationstage of the process can be carried out in a batchwise or in acontinuous manner. A continuous process is preferred. Recycle of processstreams or treating agents to the various treating or regeneration stepsis to be considered within the scope of the invention.

Other obvious variations of the process which would occur to thoseskilled in the art are intended to be included in the scope of thedisclosure and the claims.

What is claimed is:

1. In a two-stage process for desulfurizing whole atmospheric residuumhaving an initial boiling point of about 450 F. and containing sulfur,nitrogen and metallic contaminants comprising contacting said residuumin a first stage with molten potassium hydroxide treating agentcontaining 5 to 30 Wt. percent Water based on the total reagent at atemperature in the range of 400-800 F. and then hydrotreating thepartially desulfurized residuum in the presence of a cobalt molybdatecatalyst at a temperature ranging from 550 to 900 F., a pressure rangingfrom 300 to 3000 p.s.i.g., a hydrogen charge rate of 500 to 6000s.c.f./bbl. of residuum and a space velocity of 0.2 to 2.0 volumes ofresiduum per hour per volume of catalyst, the improvement comprisingregenerating spent treating agent from the first step containing K COand K 5 by contacting the spent treating agent with H S recovered fromthe hydrotreating step, contacting the partially regenerated treatingagent containing KSH With steam at a temperature ranging from 400 to1000 F. to convert the KSH to KOH and recycling the regenerated KOH tothe first stage.

2. In a two-stage process for desulfurizing whole atmospheric residuumhaving an initial boiling point of about 450 F. and containing sulfur,nitrogen and metallic contaminants comprising contacting said residuumin a first stage with molten potassium hydroxide treating agentcontaining 5 to 30 Wt. percent Water based on the total reagent at atemperature in the range of 400-800" F. and then hydrotreating thepartially desulfurized residuum in the presence of a cobalt molybdatecatalyst at a temperature ranging from 550 to 900 F., a. pressureranging from 300 to 3000 p.s.i.g., a hydrogen charge rate of 500 to 6000s.c.f./bbl. of residuum and a space velocity of 0.2 to 2.0 volumes ofresiduum per hour per volume of catalyst, the improvement comprisingregenerating spent treating agent from the first step containing K COand K S by contacting the spent treating agent in a first regenerationzone with H 8 recovered from the hydrotreating step, contacting thepartially regenerated treating agent in a second regeneration zone Witha finely divided solid compound selected from the group consisting ofMe, MeO, MeOH, wherein Me is selected from the group consisting ofcopper, nickel, iron, manganese, cobalt, calcium, magnesium, molybdenum,lead, tin and zinc, and recycling the regenerated KOH to the firststage.

3. A two-stage process for removing sulfur, nitrogen and metalimpurities from a topped crude oil having an initial boiling point ofabout 450 F. comprising the steps of contacting the oil With a treatingagent consisting of molten alkali metal hydrogen containing: 5 to 30 Wt.percent Water at a temperature in the range of 400-800" E,hydrodesulfurizing the partially purified oil at a temperature in therange of 550900 F. in the presence of 500-6000 s.c.f./bbl. of hydrogenand a hydrodesulfurization catalyst, recovering desulfurized oil, andemploying H S recovered from the hydrodesulfurization step in theregeneration of the treating agent when it has become spent.

References Cited UNITED STATES PATENTS 2,717,858 9/1955 Bronson et al.208-229 2,984,617 5/1961 De Chellis et al 208-2ll 3,164,545 1/1965Mattox 208-230 SAMUEL P. JONES, Primary Examiner.

1. IN A TWO-STAGE PROCESS FOR DESULFURIZING WHOLE ATMOSPHERIC RESIDUUMHAVING AN INITIAL BOILING POINT OF ABOUT 450*F. AND CONTAINING SULFUR,NITROGEN AND METALLIC CONTAMINANTS COMPRISING CONTACTING SAID RESIDUUMIN A FIRST STAGE WITH MOLTEN POTASSIUM HYDROXIDE TREATING AGENTCONTAINING 5 TO 30 WT. PERCENT WATER BASED ON THE TOTAL REAGENT AT ATEMPERATURE IN THE RANGE OF 400-800*F. AND THEN HYDROTREATING THEPARTIALLY DESULFURIZED RESIDUUM IN THE PRESENCE OF A COBALT MOLYBDATECATALYST AT A TEMPERATURE RANGING FROM 550 TO 900*F., A PRESSURE RANGINGFROM 300 TO 3000 P.S.I.G., A HYDROGEN CHARGE RATE OF 500 TO 6000S.C.F./BBL. OF RESIDUUM AND A SPACE VELOCITY OF 0.2 TO 2.0 VOLUMES OFRESIDUUM PER HOUR PER VOLUME OF CATALYST, THE IMPROVEMENT COMPRISINGREGENERATING SPENT TREATING AGENT FROM THE FIRST STEP CONTAINING K2CO3AND K2S BY CONTACTING THE SPENT TREATING AGENT WITH H2S RECOVERED FROMTHE HYDROTREATING STEP, CONTACTING THE PARTIALLY REGENERATED TREATINGAGENT CONTAINING KSH WITH STEAM AT A TEMPERATURE RANGING FROM 400 TO1000*F. TO CONVERT THE KSH TO KOH AND RECYCLING THE REGENERATED KOH TOTHE FIRST STAGE.